WASHINGTON (Reuters) - Investigators found additional human remains in early November of U.S. Army Sergeant La David Johnson, who was killed in an ambush last month in Niger along with three other U.S. soldiers, the Pentagon said on Tuesday.

The ambush drew attention to the little-known U.S. military presence in Niger, and it came under further scrutiny when President Donald Trump’s handling of condolence messages to the families of the dead U.S. soldiers was criticized by lawmakers in Washington.

Investigators found the remains on Nov. 12 and military medical examiners have verified that the remains were Johnson's, Pentagon spokeswoman Dana White said in a statement.

White did not identify what the remains were, but said they were discovered "at the site where Sgt. La David T. Johnson's body was recovered following the Oct. 4 attack."

The ambush, which U.S. officials believe was carried out by a local Islamic State affiliate, has thrown a spotlight on the U.S. counterterrorism mission in the West African country.

The team that was attacked in the ambush was made up of a dozen U.S. soldiers and 30 Nigerien forces on a reconnaissance mission near the village of Tongo Tongo.

An investigation into the incident is expected to be completed in January. A number of key questions still remain unanswered.

Investigators are trying to find out why U.S. forces on the ground waited an hour after the attack began before calling for support, what type of intelligence was used in the mission and why it took almost two days for the initial discovery of Johnson's body.

In an interview after the incident, Johnson's widow said she has been told little about how her husband was killed and had not been allowed to see his body.